Oil compositions

ABSTRACT

The gelling tendency of lubricating oil solutions containing selectively hydrogenated random styrene/butadiene copolymers is minimized by the presence of a polyester of an olefinically unsaturated acid.

United States Patent [1 1 Small et al.

[451 Nov. 13, 1973 OIL COMPOSITIONS Inventors: Norman J. H. Small,Christleton,

near Chester, England; Christopher J. Edhouse, Gresford, near Wrexham,Wales Assignee: Shell Oil Company, Houston, Tex.

Filed: Feb. 24, 1972 Appl. No.: 229,161

Foreign Application Priority Data Mar. 5, 1971 Great Britain 6,133/71US. Cl. 252/56 R, 252/59 Int. Cl Cl0m 1/28 Field of Search 252/59, 56 R;

Primary Examiner-Daniel E. Wyman Assistant Examiner-W. CannonAttorney-Martin S. Baer et al.

[5 7] ABSTRACT The gelling tendency of lubricating oil solutionscontaining selectively hydrogenated random styrene/- butadienecopolymers is minimized by the presence of a polyester of anolefinically unsaturated acid.

7 Claims, No Drawings OIL COMPOSITIONS The present invention relates tooil compositions and their preparation.

BACKGROUND OF THE INVENTION It is known that the viscosity oflubricating oils varies with temperature. The temperature-viscosityrelationship of an oil can be expressed by the so-called viscosity index(VI). which can be determined according to the ASTM-D2270 method. Thehigher the VI of an oil, the less the dependence of its viscosity ontemperature. In general, the VI of lubricating oils obtained byconventional processes from mineral oils is not high enough to enablesuch lubricating oils to meet the very high demands with respect toviscosity made thereon in modern automotive engines. For this reasonadditives have been proposed, which, when added to a lubricating oil,increase the VI thereof. These additives, which in most cases arepolymeric compounds, are called VI improvers.

A particularly suitable kind of VI improver is constituted by thehydrogenated butadiene-styrene copolymers which are random copolymers ofbutadiene and styrene containing 30-44 percent w of units derived frombutadiene and 5670 percent w of units derived from styrene, whichcopolymers have been hydrogenated until at least 95 percent of theolefinic double bonds and at most 5 percent of the aromatic unsaturationhas been saturated.

In view of the physical nature of such hydrogenated butadienestyrenecopolymers and the fact that intensive mixing with the aid of equipment,for example, a Silverson mixer, which provides adequate shearingactivity, is necessary in order to dissolve the hydrogenatedbutadienestyrene copolymers in the oils, it is advantageous to use themaster-batch technique for the preparation of the ultimate, improved VIlubricating oils. In this way oil composition concentrates are prepared,and these concentrates are used to prepare lubricating oil compositionscontaining a desired amount of hydrogenated butadiene-styrene copolymerby blending the concentrate with the required amount of lubricating oil.I

Usually such concentrates will contain the maximum amount ofhydrogenated butadiene-styrene copolymer which can be so handled,although flow problems with concentrates containing more than about20-25 percent w of the hydrogenated butadiene-styrene copolymer, even atsomewhat elevated temperatures, limit the maximum amount of hydrogenatedbutadiene-styrene copolymer which can be present in practice in theconcentrates. A further handling problem with such concentrates, whichcontain amount lower than 20 percent w of hydrogenated butadiene-styrenecopolymer, e.g., percent w, arises from their tendency to gel onstorage. The time needed for the concentrates to gel depends on thetemperature of storage and may vary from 2 hours (e.g., on storage atabout 50C) to 2 weeks or longer (e.g., on storage at about C). Ifgelling occurs, the concentrate cannot easily be removed from thecontainer such as a storage tank, a barrel or a railway tank wagon.

It has now been found in accordance with the present invention thatgelling can be avoided or at least signficantly reduced by theincorporation of additional polymer compounds in the concentrates.

LII

According to the present invention there is provided an oil compositionwhich comprises:

1. a lubricating oil,

2. a random copolymer of butadiene and styrene containing 30-44 percentw of units derived from butadiene and 56-70 percent w of units derivedfrom styrene, which copolymer has been hydrogenated until at least 95percent of the olefinic double bonds and at most 5 percent of thearomatic unsaturation has been saturated, and

3. an oil-soluble polyester which comprises molecular units derived froman alkyl ester of an a-olefinically unsaturated carboxylic acid in whichthe alkyl chain or chains contain(s) at least 7 carbon atoms.

The present invention also includes a lubricating oil formed by admixingan oil composition as just defined with the same or a differentlubricating oil.

The random copolymer of butadiene and styrene may be obtained in anyknown or suitable manner. Thus it maybe obtained by copolymerization ofbutadiene and styrene in emulsion, but preferably the copolymerizationis carried out in solution with the aid of an alkali metal or analkalimetal-hydrocarbon, preferably lithium metal or aIithiumhydrocarbon, as a catalyst. Lithium alkyls, such as ethyllithium, propyl lithium, hexyl lithium and, in particular, sec-butyllithium, are suitable. The solvent for such solution copolymerizationmay be a liquid which is inert under the conditions prevailing duringthe copolymerization, and may be an aliphatic hydrocarbon such aspentane, hexane, cyclohexane or methylcyclohexane or an aromatichydrocarbon such as benzene, toluene or xylenes. Mixtures of two or morehydrocarbons may also be used. Random copolymers of butadiene andstyrene, which do not contain large blocks of one or both of the monomers, are made if a polar compound which does not inactivate thecatalyst and which brings about a tendency to random copolymerization ispresent during the polymerization. Examples of such compounds are tert.amines and ethers, for example, diethylether, dibutylether, anisole,and, in particular, tetrahydrofuran. The amount of polar compound usedmay lie between wide limits and may range, for instance, from 0.05 to 50percent w, preferably from 0.1 to 10 percent w, of the total solvent.The copolymerization may be carried out at a temperature between 20 andC and under a pressure which is at least sufficient to maintain themonomers and the solvent in the liquid phase.

The molecular weight of the random copolymer of butadiene and styreneemployed, in hydrogenated form, in carrying out the present inventionmay lie between wide limits; in general a copolymer with a kineticmolecular weight between 40,000 and 100,000 may be used. Thehydrogenation of the random copolymers of butadiene and styrene can becarried out with any catalyst, which gives rise to saturation of atleast percent of the olefinic double bonds and has a minimum influenceon aromatic unsaturation. Examples of such catalyst are catalystscontaining a non-noble metal of Group VIII of the Periodic Table or acompound thereof, e.g., Raney nickel, or nickel on kieselguhr.Preferenceis given to hydrogenation catalysts obtained by reacting analuminium trialkyl (e.g., aluminium triisobutyl) with a nickel salt ofan organic acid (e.g., 2- ethyl hexanoic acid). After removal ofsolvents and/or other volatile material, the hydrogenatedbutadienestyrene copolymers are obtained in the form of solid rubberymaterials, which, in order to facilitate their solution in oil, may bereduced to crumb form by mechanical means.

Although the oilsoluble polyester additives used in carrying out thepresent invention may be derived from the alkyl esters of a-olefinicallyunsaturated polyor dicarboxylic acids, such as maleic acid or fumaricacid, it is prefered to employ polyesters derived from the alkyl estersof a-olefinically unsaturated monocarboxylic acids such as acrylic acidand, in particular, methacrylic acid. The alkyl chains of the estergroups may contain up to any desired number of carbon atoms, but ingeneral esters containing from 7 to 24, in particular from 9 to 18,carbon atoms in the alkyl chains are suitable.

it is often of advantage to use oil-soluble polyesters derived frommixtures of said alkylesters of aolefinically unsaturated carboxylicacids, said. mixtures containing esters of different alkyl cahin length.In particular polyesters derived from mixtures of esters containing anaverage number of carbon atoms in the alkyl chains of from 12 to 15 maybe used.

The alkyl chains of said esters may be straight or they may be branched.Esters having straight alkyl chains may be derived from naturalalcohols, while those having branched alkyl chains may be derived fromsynthetic alcohols which may be synthesized, for example, by a reactionof one or more olefins with carbon monoxide and hydrogen in the presenceof a catalyst such as a complex catalyst consisting of cobalt, carbonmonoxide and optionally a phosphorus compound.

The oil-soluble polyesters may also contain in their molecularstructures polymer units derived from monomers other than saidalkylesters of a-olefinically unstaurated carboxylic acids. For example,such other monomers may be alkyl esters of said acids, which esters havealkyl chains having less than 7 carbon atoms (e.g., methylmethacrylate).or esters of said acids containing polar groups such as hydroxyl groups(e.g., B-hydroxyethylmethacrylate) or amine groups (such as di-ethylamino ethylmethacrylate), said acids advantageously being monocarboxylicacids as exemplified.

The oil-soluble polyesters may also contain in their molecularstructures polymer units derived from other esters, e.g., vinyl esters,such as vinylacetate, or derived from other types of monomers, such asN- vinylprolidone, 4-vinylpyridine or 2-methyl-5- vinylpyridine.

The oil-soluble polyesters may be prepared in any way desired; forexample, polymerization or copolymerization under free radicalpolymerization conditions is usually suitable. It is also possible toprepared such polyesters indirectly by introducing the required alkychains containing at least 7 carbon atoms into the molecular structuresof existing polymers and copolymers. For example, polymers may beprepared containing in the molecule repeating units derived froma-olefinieally unsaturated carboxylic acids and the carboxylic acidgroups thereof may be esterified by reaction with alcohols containing atleast 7 carbon atoms in their molecules. The polymers have averagemolecular weights between about 20,000 and 1 million.

The lubricating oils which can be used in forming oil compositionsaccording to the present invention may be synthetic lubricating oils(e.g., ester oils) or mineral lubricating oils. Since in most cases theoil compositions of the invention will be used to prepare high viscosityindex oils based on mineral lubricating oils, it is of advantage in suchcases to form the oil compositions from lubricating oils which willconstitute the mineral lubricating oil component (or one of suchcomponents) of the high V.l. lubricating oil eventually to be prepared.

The amount of hydrogenated random butadienestyrene copolymer componentin an oil composition in accordance with the present invention may be upto 20-25 percent w thereof, and preferably is from 5 to 20 percent wthereof.

The amount of the oil-soluble polyester component of said oilcompositions may lie between wide limits. in general, amounts off from0.05 to 1.0 percent w, in particular from 0.1 to 0.5 percent w thereof,may be employed. Such oil-soluble polyesters can be easily dissolved inmineral or synthetic oils, and may be made available in the form of 3050percent w concentrates in such oils.

Oil compositions in accordance with the present invention may beprepared by intimately mixing all components e.g., with the aid ofmixing equipment having shearing activity, such as a Silverson mixer. ltis also possible, however, to mix a hydrogenated butadienestyrenecopolymer with oil in such equipment, and subsequently to blend thesolution obtained with a solution of an oil-soluble polyester in alubricating oil.

lf desired, the oil compositions of the present invention may alsocomprise compounds which are required in the ultimate lubricating oils,such as detergent additives, (e.g., calcium petroleum sulphonates,calcium salts of alkylsalicylic acids, polyamines containing ahydrocarbon chain with at least 50 carbon atoms, such aspolyisobutenyl-tetraethylenepentamine), extreme pres sure (E.P.)additives (e.g., Zinc dialkyl dithiophosphates) and others.

The ultimate lubricating oil compositions suitable to be used in enginescan be prepared from the oil compositions according to the invention byadmixing with a lubricating oil, and if desired addition of additives,such as those mentioned in the preceding paragraph.

The present invention may be illustrated by the following example:

EXAMPLE A hydrogenated random copolymer of butadiene and styrene, whichcontained 59 percent w of styrene and which polymer was practically freeof olefinic unsatu ration, was dissolved in a HVl 60 oil with the aidofa Silverson mixer to a concentration of 10 percent w.

The resulting solution was blended with solutions in lubricating oil oftwo different polyester additives viz. a polyalkylmethacrylate withalkyl chains with at least 9 carbon atoms and an average of l4 carbonatoms per alkyl chain (additive A) and a copolymer oflaurylmethacrylate, stearylmethacrylate and andB-hydroxyethylemethacrylate in a molar ratio 8 2 1.8 (additive B), togive three oil compositions in accordance with the present inventioncontaining 0.2 and 0.4 percent w of additive A and 0.2 percent w ofadditive H, respectively.

The oil solution containing only the hydrogenated random copolymer ofbutadiene and styrene and the oil compositions containing the additivesA and B were stored at 50C for various periods. The following tableshows that all the compositions in accordance with the present inventionremained free flowing after two days.

The compositions containing 0.2 percent w of the additives A and Bpartly gelled after some time, but that the composition containing 0.4percent of the additive A was free flowing even after 3 weeks.

TABLE Time of inspection after blending 2 days l week 2 weeks 3 weeksSolution of gelled gelled gelled gelled random copolymer solution of 4-free partially partially partially 0.2% additive A flowing gelled gelledgelled Solution of free partially partially partially 0.2% additive Bflowing gelled gelled gelled Solution of free free free free 0.4%additive A flowing flowing flowing flowing c. 0.05 to 1.0 percent byweight of an oil-soluble polyester which comprises molecular unitsderived from an alkyl ester of an acrylic acid in which the alkyl chainor chains contain(s) at least 7 carbon atoms, said polyester having anaverage molecular weight between about 20,000 and one million.

2. An oil composition according to claim 1 in which the kineticmolecular weight of the random copolymer is between 40,000 and 100,000.

3. An oil composition according to claim 1 in which the acid ismethacrylic acid.

4. An oil composition according to claim 1 in which the alkyl chains inthe polyester contain from 9 to 18 carbon atoms.

5. An oil composition according to claim 1 in which the polyester isderived from mixtures of esters containing an average number of carbonatoms in the alkyl chains of from 12 to 15.

6. An oil composition according to claim 1 in which the amount ofhydrogenated random butadiene-styrene copolymer is from 5 to 20 percentw thereof.

7. An oil composition according to claim 1 in which the amount ofoil-soluble polyester is from 0.l to 0.5

percent w thereof.

2. An oil composition according to claim 1 in which the kineticmolecular weight of the random copolymer is between 40, 000 and 100,000.3. An oil composition according to claim 1 in which the acid ismethacrylic acid.
 4. An oil composition according to claim 1 in whichthe alkyl chains in the polyester contain from 9 to 18 carbon atoms. 5.An oil composition according to claim 1 in which the polyester isderived from mixtures of esters containing an average number of carbonatoms in the alkyl chains of from 12 to
 15. 6. An oil compositionaccording to claim 1 in which the amount of hydrogenated randombutadiene-styrene copolymer is from 5 to 20 percent w thereof.
 7. An oilcomposition according to claim 1 in which the amount of oil-solublepolyester is from 0.1 to 0.5 percent w thereof.